This invention relates to an instrument for use in applying surgical fasteners such as staples, clips and the like to living tissue. More particularly, the invention relates to a surgical stapling instrument for use in forming a plurality of laterally spaced rows of staples in an internal body organ. Typically, such an instrument comprises a pair of cooperating elongate jaw members. In use, one jaw member carries a staple cartridge with at least two laterally spaced rows of staples, and the other carries an anvil with staple-closing depressions aligned with the rows of staples in the cartridge. In the type of instrument to which the invention pertains, a pusher bar assembly is moved longitudinally along the jaws to eject staples from the cartridge sequentially by means of a camming action effected by cooperation of the forward end of the pusher bars with staple pushers carried by the cartridge in association with the individual staples. The camming action closes the staples against the anvil, forming laterally spaced lines of staples in tissue gripped between the jaws trailing the pusher bars.
In instruments of this kind, a knife is often associated with the pusher bars in such a manner as to move forward along the jaws in tandem with, but slightly behind, the pusher bars. As the pusher bar and knife assembly is moved forward, the knife cuts the tissue along a line between the staple rows. By way of example, one instrument of this type is disclosed in U.S. Pat. No. 3,499,591, commonly assigned herewith, the disclosure of which is incorporated herein by reference. (The discussion hereinafter of surgical staplers refers consistently to a "pusher bar and knife assembly", but, except for references to cutting of the tissue, is uniformly applicable to a stapler having no knife.)
The staple cartridges, anvils and pusher bar and knife assemblies have commonly been made of disposable plastics and low cost metal stampings, while the frames have more generally been constructed for repeated use and must be resterilized before each reuse. A surgical stapler must be cleaned and sterilized with great care to ensure that every portion of the instrument has been made aseptic, and hospital sterilization of such an instrument is a difficult and painstaking procedure.
In recent years, in order to obviate the need for repeated sterilization of instruments, the tendency in the surgical field has been toward the introduction of fully self-contained disposable instruments which are used for only a single operation and then discarded. Obviously, economics is a factor in the design of such disposable instruments, and it is desirable to design such instruments to use the lightest possible readily available, economical materials and to employ the most economical possible production techniques.
With stapling instruments of the type described, relatively large forces are involved in clamping the tissue to be fastened and in ejecting the individual staples, forcing them through the gripped tissue and closing them against the anvil. Such forces tend both to separate the jaws vertically and to distort the jaws laterally, thereby hindering accurate stapling. Although in instruments of heavy materials like steel this problem does not make the instrument either unreliable or difficult to use, this problem is of somewhat greater significance when lightweight, disposable materials are used for the manufacture of the jaw frames.